1. Field of the Invention
This invention relates to a plug-in unit-mounting structure and an electronic apparatus, and more particularly to a plug-in unit-mounting structure for mounting plug-in units having various circuit packages mounted on printed circuit boards thereof, and an electronic apparatus.
2. Description of the Related Art
Electronic apparatuses for communication, such as transmitters and switchboards, use a bookshelf-type electronic apparatus in which a plurality of printed circuit board units (hereinafter referred to as “plug-in units (PIUS) each having electronic circuit packages are vertically mounted on a back wiring board (BWB) mounted on the rear face of a metal shelf thereof. The PIU comprises a printed circuit board and a plurality of electronic circuit packages each formed with electronic circuits, such as LSIs (Large-Scale Integrated circuits), mounted on the printed circuit board. There have been already proposed several plug-in unit-mounting techniques for mounting PIUs on the BWB.
FIG. 13 is a front view of an example of a plug-in unit-mounting structure.
In a metal shelf 100, respective sets of substantially C-shaped upper and lower guide rails 103a and 103b are secured to upper and lower sides 101 and 102 thereof in a manner opposed to each other at equally-spaced intervals. Box-shaped full-size PIUs 104 can be vertically mounted in the metal shelf 100 using the upper guide rails 103a and the lower guide rails 103b as guides. Further, center rails 105 are provided between associated ones of the upper and lower guide rail 103a and 103b of the metal shelf 100 as intermediate guide members. With this arrangement, half-size box-shaped PIUs 106 can be vertically mounted at respective upper shelves of the metal shelf 100 using the upper guide rails 103a and the center rails 105 as guides. Similarly, half-size box-shaped PIUs 107 can be mounted at respective lower shelves using the center rails 105 and the lower guide rails 103b as guides (see e.g. the pamphlet of International Publication WO 00/074454 (Section of [Brief Description of the Construction of Telecommunications Apparatus 10] in PREFERRED EMBODIMENTS FOR WORKING THE INVENTION, and FIG. 1)).
Thus, PIUs 104, 106 and 107 having different sizes can be mounted on the BWB (not shown) of the metal shelf 100 shown in FIG. 13, and hence it is possible to simplify the design of e.g. a package-type communication apparatus, which improves not only economy but also the convenience of maintenance.
FIG. 14 is a front view of another example of the plug-in unit-mounting structure.
In a metal shelf 200, guide rails 202 are not mounted on the upper and lower sides, but are mounted on a BWB 201 in a cantilever manner such that they protrude forward and are inwardly opposed to each other. Box-shaped PIUs 203 and 204 having bar-shaped guides (not shown) mounted along two opposed sides which are orthogonal to a side where connectors are mounted can be vertically mounted in the metal shelf 200 using the guide rails 202 as guides. The vertical distances between locations where the guide rails 202 are mounted are determined in a manner adapted to the sizes of the PIUs to be mounted (see e.g. Japanese Unexamined Patent Publication No. H04-113693 (fourth and fifth pages, and FIGS. 1 and 3).
Thus, the metal shelf 200 shown in FIG. 14 is configured such that the guide rails 202 are mounted on the BWB 201 in a manner adapted to the sizes of the PIUs 203 and 204 having different sizes. Therefore, the PIUs 203 and 204 can be mounted on the metal shelf 200 in high density without the waste of space.
FIG. 15 is a front view of still another example of the plug-in unit-mounting structure.
Respective sets of substantially C-shaped guide rails 303a and 303b are secured to an upper side 301 and a lower side 302 of a metal shelf 300 in a manner opposed to each other. Printed circuit board-type full-size PIUs 304 can be vertically mounted on the metal shelf 300 using the guide rails 303a and 303b as guides. Further, some of the guide rails 303a and 303b secured to the metal shelf 300 hold mounting frames 305 for the PIUs 306 and 307. Each mounting frame 305 has center rails 305a and 305b integrally formed therewith, and grooves 305c formed in the top and bottom thereof, for engagement with the guide rails 303a and 303b (see e.g. Japanese Unexamined Patent Publication No. 2005-277281 (Paragraph Numbers [0010] to [0024] and FIG. 1)).
As described above, in the metal shelf 300 shown in FIG. 15, by using the mounting frame 305, half-size PIUs 306 of printed circuit board type can be mounted at upper shelves by each being guided between the guide rail 303a and the center rail 305a of the mounting frame 305. Similarly, half-size PIUs 307 of printed circuit board type other than those 306 can be also mounted on lower shelves by each being guided between the guide rail 303b and the center rail 305b of the mounting frame 305.
In the illustrated example, only by fixing the guide rails 303a and 303b to opposed sides of the metal shelf 300, it is possible to cope with PIUs having different sizes. Therefore, as distinct from the case of the metal shelf 100 shown in FIG. 13, it is not necessary to provide the center rails 105 thereto as the intermediate guide members, which makes it possible to perform high-density mounting using a smaller number of components. Further, as distinct from the metal shelf 200 shown in FIG. 14, it is not required to mount each guide rail 202 on the BWB 201 in a manner adapted to the size of a PIU 203. Therefore, even when the PIUs 304, 306 and 307 already mounted in the metal shelf 300 are replaced by PIUs having different sizes, it is possible to easily mount PIUs having desired widths at predetermined locations.
However, in both of the above-described plug-in unit structure shown in FIGS. 13 and 15, the guide rails for guiding the PIUs to the BWB are mounted on the metal shelves themselves. In general, the number of layers of a printed circuit board increases or decreases depending on the amount of wiring, and hence as the amount of wiring becomes larger, the size of the printed circuit board in the direction of the thickness thereof inevitably tends to increase. Therefore, in the cases of the metal shelves 100 and 300, there is a problem that existing guide rails are not suitable for the mounting of a PIU on which is mounted a different printed circuit board increased in size in the direction of thickness thereof and having a larger amount of wiring.
Further, in the case of the metal shelf 300 shown in FIG. 15, if a PIU has a different thickness, as in the case of a PIU in which a heat sink provided with a radiation fin is arranged on a printed circuit board, it is not easy to mount the PIU on the metal shelf 300. What is more, when mounting a box-shaped PIU without containing a printed circuit board to begin with, it is required to provide guide rails for guiding the box-shaped PIU in place of the fixed guide rails 303a and 303b. 
On the other hand, the FIG. 14 metal shelf 200 for mounting the box-shaped PIUs 203 and 204 is adapted only to the box-shaped PIUs 203 and 204, and hence it is impossible to mount PIUs having a printed circuit board exposed without being covered with a box-shaped covering. Further, since the opposed guide rails 202 are separately fixed to the BWB 201, and hence, the distance between the opposed guide rails is sometimes not uniform due to variations of parts thereof.
As described above, the above-described electronic apparatuses suffer from the problem that it is not easy to replace PIUs mounted on a shelf or increase or reduce the number of mounting frames e.g. when changing the design of the apparatuses.